Fix the last remaining races in fyne_demo

[Jacalz]

Description:

This adds appropriate safety in goroutines and also moves the advanced tab to only redraw when settings actually change (it was drawing each second before and wasting CPU time). I clicked through all the tabs now and can no longer see any races reported.

For #4654
Fixes #4568

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

[andydotxyz]

Thanks so much for this Jacob.

Just a quick question - are you sure it will update with changes to texture scale? (When a window drags to a non-retina screen on macOS...
I think that's why the timer was there.

[Jacalz]

Good point. I think it also will be wrong when just dragging between two windows with different DPI, right? I'll change the code to only refresh the widgets when scale changes instead :)

[dweymouth]

I think @andydotxyz was talking about the label that shows the scale info, not the widgets themselves not getting redrawn? The driver handles refreshing the window when the scale changes.

[coveralls]

coverage: 59.374% (+0.06%) from 59.316%
when pulling 73d0cbf on Jacalz:fix-demo-races
into e6225b5 on fyne-io:develop.

[Jacalz]

I think @andydotxyz was talking about the label that shows the scale info, not the widgets themselves not getting redrawn? The driver handles refreshing the window when the scale changes.

Indeed, I know. I just meant that I would try to make the existing code a bit faster by not redrawing/refreshing them when the scale hasn't changed. I'm not a huge fan of an infinite loop with refresh each second.

[andydotxyz]

I guess just be careful because texScale is not a scale change, it's an internal detail to the GLFW windows...

[Jacalz]

I ended up just moving to the old once per second update but tidied up the code a bit.

[andydotxyz]

Nice use of the animation construct :)

[Jacalz]

Thanks. I was rather happy with the one as well. Haven't used it before actually. Now we're just trying to get the flaky Ubuntu test to work :)